Electroplating nickel and electrolyte therefor



United States Patent Office 3,39,iifi2 Patented June 25, 1968 ABSTRACT OF THE DISCLOSURE An electrolyte and process for the electrodeposition of nickel. The electrolyte contains a compound providing sulfohydrocarbon-di-yl neocarboxyl-ate anion wherein R R and R are alkyl groups and R is a hydrocarbon-di-yl group containing at least 2 carbon atoms. The compound acts to reduce surface tension of the electrolyte, thereby reducing the tendency toward production of pitted deposits.

This invention relates to the electrodeposi'tion of nickel. More particularly this invention relates to compositions which may be used as surfactants and in electrodeposition of nickel.

As is well known to those skille-d-in-the-art, the electrodeposition of nickel may commonly be carried out from nickel plating solutions or baths containing at least one nickel compound providing nickel ions together with various additives including primary brighteners, secondary brighteners, secondary auxiliary brighteners, etc. These solutions typically may contain surfactants, detergents,

dispersants, etc., to depress the surface tension and reduce pitting at the cathode surface.

It is an object of this invention to provide a novel process for electrodeposition of nickel. It is a further object of this invention to provide a novel nickel plating bath containing a novel surfactant which is highly resistant to hydrolysis, highly water soluble, and which will reduce surface tension.

It is an object of this invention to provide novel sulfohydrocarbon-di-y-l neocarboxylate compositions which may be employed as surfactants in metal finishing, metal electroplating, pesticides, and in heavy duty cleaning processes. These surfactants may be highly water soluble, highly resistant to alkaline or acid hydrolysis, and when present even in small amounts may greatly reduce surface tension as e.g. in nickel electroplating baths.

Other objects and advantages will be obvious to those skilled-in-the-art after inspection of the following description.

In accordance with certain of its aspects, the novel process of this invention for electrodepositing nickel onto a basis metal may comprise passing current from an anode to a basis metal cathode through an aqueous acidic nickel plating solution containing at least one nickel compound providing nickel ions for electrodepositing nickel and containing as a surfactant a compound which provides sulfohydrocarbon-diyl-neocarboxylate anion llii R2-( 3o0o-R-sotwherein R R and R are alkyl groups and R is a hydrocarbon di-yl group containing at least two carbon atoms.

A neocarboxylate is derived from a neocarboxylic acid i.e. an acid having a tertiary carbon atom a to a carboxylic group, viz. having a carbon atom connected directly to four other carbon atoms, one of which is a component of a carboxylic group.

Nickel plating may be carried out in accordance with this invention from baths containing at least one nickel compound providing nickel ions for electrodepositing nickel. Typically this compound may be a nickel salt such as nickel sulfate, nickel chloride, nickel sulfamate, nickel fluoborate etc., and the bath employed may be a Watts bath, a high chloride bath, a sulfamate bath, a sulfamatechloride bath, etc. A preferred bath may be a Watts bath, having an electro'metric pH of 4.0, and containing, in aqueous solution, 300 g./l. nickel sulfate, 60 g./l. nickel chloride, and 45 g./'l. boric acid.

These baths may be used with the compounds of the invention without brightening additives as when employed in techniques such as nickel electroforming, decorative plating, or building up of worn parts or may contain other ingredients to obtain bright, leveled, and ductile deposits. These ingredients may include primary brighteners as are known in the art, e.g. acetylenic, N-heterocyclic, active sulfur, etc., primary brighteners, secondary brighteners as are known in the art, e.g. aryl sulfonates, aryl sulfonamides, etc.; and secondary auxiliary brighteners as are known in the art, e.g. sodium allyl sulfonate, sodium 3- chloro-Z-butene sulfonate-l, etc. In duplex nickel plating processes in which corrosion effects are minimized, the bath-compatible surfactants of this invention may be used in semi-bright as well as bright nickel plating baths.

Plating may be effected by passing direct current from the anode to the cathode through the aqueous solution containing the nickel ions and the novel surfactant. Typically, in certain nickel plating baths, the solution or bath maybe maintained at temperatures of 40 C. C., say 55 C. Agitation maybe provided by air or mechanically as by a moving cathode bar. Current density during electroplating may be 2-10, say 5 amperes per square decimeter (a.s.d.). Plating may typically be carried out for 10-60, say 30 minutes.

The anode which may be used may be a soluble anode, typically nickel, or an insoluble anode, typically lead. The cathode may include basis metals such as ferrous metals, as steel, copper, including alloys thereof as brass or bronze, zinc, etc. Typically, it may bear a first plate of copper and a plate of semi-bright nickel.

Small amounts of the additives may reduce the surface tension to about 40 dynes/ cm. which is sufiicient to prevent pitting of the plated metal. As little as 0.125 g./l. of the additive effectively reduces pitting. The preferred amount of surfactant additive may be 0.125-2 g./l., say 0.75 g./l.

The novel surfactant obtained, according to certain aspects of this invention, may be a sulfohydrocarbon-di-yl neocarboxylate compound having the formula wherein R R and R are each alkyl groups; R is a hydrocarbon-di-yl group containing at least 2 carbon atoms; and M is a cation. Typically M may be hydrogen, an alkali metal, preferably sodium or potassium, a polyvalent metal such as an alkaline earth metal, preferably calcium or strontium, nickel, cobalt and copper, and ammonium including substituted and unsubstituted ammonium. Preferred substituted ammonium cation may include a tertiary ammonium cation, e.g. triethanolarnmonium, trilaurylammonium, trimethanolammonium, methanoldiethanolammonium, etc. For use in baths from which 3 metals are electrodeposited, the compound is bath-compatible and provides the novel anion. In this aspect of the invention, M may preferably be alkali metal, e.g. sodium or potassium or the same as the metal being electrodeposited. These include nickel, cobalt, copper, etc.

It is apparent that when M is polyvalent, the valences thereof may be satisfied by linkage to more than one sulfohydrocarbon-di-yl neocarboxylate group. Thus when M is a divalent metal, e.g., nickel, the corresponding bis salts may be formed.

Typical preferred specific sulfohydrocarbon-di-yl neo carboxylates which may be used in the practice of this invention may include:

TABLE I Acid 3-sulfopropylpivalate Sodium 3-sulfopropylpivalate Potassium 3-sulfopropylpivalate Triethanolammonium 3-sulfopr0pylpivalate Nickel bis-(3-sulfopropylpivalate) Potassium 3-sulfopropyl neo-nonanoate Sodium 3-sulfopropyl neo-nonanoate Potassium Z-sulfopropyl neo-nonanoate Potassium 3-sulfobutyl neo-nonanoate Triethanolammonium 3-sulfopropyl neo-nonanoate Triethanolammonium 2-sulfopropyl neo-nonanoate Nickel bis-(3-sulfopropyl neo-decanoate) Potassium 3-sulfopropyl neo-pentadecanoate Potassium 3-sulfopropyl neo-heptadecanoate Triethanolammonium 3-sulfopropyl neo-nonadecanoate Triethanolammonium 4-sulfobutylpivalate Potassium 4-sulfobutyl neo-nonanoate Potassium 3-sulfopropyl neo-heptanoate Potassium 3-sulfopropyl neo-tridecanoate It will be apparent that the cations employed in the i table may be replaced by other cations.

Pivalates are derived from pivalic acid which has the structure (3H HaC-C-COOH Other typical neocarboxylic acids from which neocarboxylate esters of this invention may be prepared may be those commercially available as Enjay neocarboxylic acids and as Versatic acid esters typically derived from mixtures of higher neocarboxylic acids containing more than 5 and typically 6-19 carbon atoms, sold under the trademark Versatic.

A commercial mixture of 7 carbon neocarboxylic acids (neo-heptanoic acids), may contain neocarboxylic acids having the structure If R(|JCOOH wherein R, R", and R' are alkyl groups having a total of 5 carbon atoms, and may be available under the designation Enjay neo-heptanoic acid. These acids include Over 90% of the mixture may be the 2,2-dimethylpentanoic acid and the remainder may be the Z-ethyl-Z-methylbutanoic acid. This commercially available acid is a liquid and has an acid value of 431.

Another commercial mixture of 9 carbon neocarboxylic acids (neo-nonanoic acids), wherein R in the general formula and R" and R' are alkyl groups having a total of 6 carbon atoms, may be available under the designation Versatic 9 acid. These acids include CH CH 11 0-543 Il -0 o 011 and This commercially available acid is a liquid which is immiscible in Water and has an acid value of 343.

Another commercially available acid which is a mixture of 911 carbon acids (neo-nonanoic acid, neo-decanoic acid, and neo-undecanoic acid) may contain neocarboxylic acids having the structure:

wherein R and R" may be alkyl groups having a total of 6-8 carbon atoms. This acid may be prepared by the reaction of olefins, Water, and carbon monoxide in the presence of a strong acid catalyst. The commercial Versatic 911 acid may contain approximately neocarboxylic acid. This commercially available acid is a liquid which is immiscible in Water and has an acid value of 300. It further has a refractive index n of 1.447 and solidifies below 30 C.

Another commercially available acid which is a mixture of 10 carbon neocarboxylic acids (neo-decanoic acids) may contain neocarboxylic acids having the structure:

wherein R, R", and R are alkyl groups having a total of 8 carbon atoms, and may be available under the designation Enjay neo-decanoic acid. The neo-carboxylic acid content of this product may be greater than Of the neo-carboxylic acids present, about 25% i5% contain methyl groups in the R and R" positions, about 60%:10% contain one methyl group in but one of the R, R", and R positions, and about 15%:10% contain alkyl groups containing at least two carbon atoms in the R, R", and R' positions.

Another commercially available acid which is a mixture of 13 carbon neocarboxylic acids (neo-tridecanoic acids) may contain neocarboxylic acids having the structure:

wherein R, R", and R' are alkyl groups having a total of 11 carbon atoms, and may be commercially available under the designation Enjay neo-tridecanoic acid. The neo-tridecanoic acid content of this product may be greater than 95%. A portion of the impurities may be homologous neo-carboxylic acids. The proportion of acids containing one or two methyl groups in the positions attached to the carbon atom alpha to the carboxylic group of Enjay neo-tridecanoic acid is similar to the proportion obtained in Enjay neo-decanoic acid.

Another commercially available acid which is a mixture of 15-19 carbon acids (neo-pentanoic acid, neohexadecanoic acid, neo-heptadecanoic acid, neo-octadecanoic acid, and neo-nonadecanoic acid) may contain neocarboxylic acids having the structure wherein R and R are alkyl groups having a total of 12-16 carbon atoms. This acid may be prepared in a similar manner to Versatic 911 acid. The commercial Versatic 1519 acid is a liquid which is immiscible with water and has an acid value of 207.

The neocarboxylic acid mixtures, as obtained commercially, particularly the acid mixtures include acids having at least 4 carbon atoms, may also contain a proportion of other materials including secondary acids and a hydrocarbon-paralfinic oil commonly known as neutral oil." The ester compositions may, if desired, be separated from the neutral oil by ether extraction. When it is desired to employ the esters as wetting agents in nickel plating baths, the neutral oil may preferably be removed.

The most preferred esters which may be used in the practice of this invention may typically be the 3-sulfopropylpivalates and the 3-sulfopropyl neo-nonanoate.

The novel compounds of this invention may, in accordance with certain of its aspects, be prepared by reacting in a solvent dispersion, (1) neocarboxylic acid, (2) an alkaline compound which provides the cation M and (3) a hydrocarbon sultone.

The reaction preferably is carried out in a solvent in which the reactants are dispersible, i.e. suspendable or soluble, and is most preferably carried out in a solvent in which the compound containing the M cation is soluble. Such solvents may typically include organic solvents such as alcohols, etc. An especially preferred solvent for the reaction is methanol.

The neocarboxylic acid employed may preferably be one of those mentioned supra, e.g. pivalic acid and higher neocarboxylic acids such as those containing more than 5 carbon atoms and typical 649 carbon atoms. Especially preferred neocarboxylic acids may include pivalic acid and mixtures of 9ll carbon neocarboxylic acids.

The alkaline compound which provides the cation M may be indicated as MX in which X is an anion typically hydroxide. M may typically be ammonium or alkali metal, e.g. sodium, potassium, lithium, etc. When ammonium is employed, it may be substituted or unsubstituted. Preferred substituted cations may include triethyl ammonium, trimethyl ammonium, trilauryl ammonium, trimethanol ammonium, methanol diethanol ammonium, etc. Commonly the cations may be present as MOH, e.g. sodium hydroxide, potassium hydroxide, lithium hydroxide etc. and most preferably sodium or potassium hydroxide, particularly when it is intend to employ the surfactants in metal plating baths.

When preparing the salts of the sulfohydrocarbon-di-yl neocarboxylates where M is not ammonium or alkali metal and particularly where M is polyvalent, it may be desirable to prepare the desired M salt by first preparing the alkali metal sulfonate salt and then passing its water solution through a cation exchange resin on the hydrogen cycle to obtain the free sulfonic acid in the eluate. The eluate may then be neutralized with the oxide, hydroxide, carbonate, etc. of the metal desired, e.g. nickel or cobalt to form the desired metal salt of the sulfonic acid.

The sultones which may be employed to prepare the novel compounds of this invention may include those containing a oarbon-oxygen sulfur-carbon linkage in a ring, the hexavalent sulfur atom being further bonded to two additional oxygen atoms. Typically such sultones may have the formula wherein R is a hydrocarbon-di-yl group containing at least two carbon atoms. The sultone which may preferably be used may contain 2-8 carbon atoms. The most preferred sultone may be 1,3-propane sultone,

although sultones such as 1,1,3-trime thyl-l,3-propane sultone 1,4-butane sultone,

and 1,3-butane sultone,

also may produce highly useful additives. The longer chain alkane sultones such as pentane sultones and octane sultones or other sultones containing several carbon atoms, such as tolyl sultones may also be used to produce additives within the scope of the invention.

The process may preferably be carried out by dispersing the acid and the alkaline compound in an alcohol and slowly adding the hydrocarbon sultone, preferably in the same solvent, to the system. It is also preferred that the addition be made while the system is at reflux, although the temperature may also be raised to reflux after the addition is complete in order to avoid some exothermic effects.

Ina preferred embodiment of the invention the neocarboxylic acid may be reacted under reflux in solvent, preferably methanol with the compound MOH, preferably potassium hydroxide and the sultone preferably 1,3- propane sultone, in about a 1:1:1 molar ratio. In practice it may be preferable to use MOH and the sultone in slight excess (up to about 5%) of the theoretical molar ratio to assure more complete reaction. It also may be desirable to keep the reaction mixture alkaline by further addition of MOI-I during the reflux period, using litmus or other suitable indicator of alkalinity. The slight excess of MOI-I and sultone may result in formation of a hydroxy sulfonate which need not be separated from the desired product.

To obtain as high a yield of product as possible it may be preferable to evolve the solvent by heating under reduced pressure. The essentially solvent-free residue may then be separated from neutral oil in the manner heretofore indicated if desired.

The product may also be separated from the solvent by the spray drying technique wherein the reaction mixture is sprayed into contact with hot air or a fluidized bed of the reaction product as independently produced to evolve solvent and give a residue of dried product.

The product of this reaction, typically that formed from pivalic acid, potassium hydroxide, and 1,3-propane sultone, may be readily recovered in high yield. In this product, it is apparent that the R group in the general formula -i.e. the basic hydrocarbon-di-yl chain (containing at least 2 carbon atoms, and preferably 2-8 carbon atoms) in the structure of the molecules of the sulfohydrocarbon-di-yl neocarboxylate, is derived from the sultone by opening of the ring. Illustrative alk-di-yl and substituted alk-di-yl R groups employed as aforesaid are ethane-1,2-di-yl; propane 1,2 di yl; propane-1,3'di-yl; butane-1,4-di-yl; butane-1,3-di-yl; pentane-1,5-di-yl; hexene-1,6-di-yl; hepheptane-l,7-di-yl; octane-1,8-di-yl; etc. Alkyl-aryl groups include pentane-l,5-di-yl; o-benzyl; m-benzyl; p-benzyl; etc. Arylene groups include phenylene; 1-me-t-hyl-2,3- phenylene; l-methyl-2,4-phenylene; 1-methyl-2,5-phenylene; etc.

The novel compounds of this invention may also be prepared by reacting a neocarboxylic acid with a hydroxy sulfonate, HO-RSO 'M, by the following reaction:

wherein R, R R R and M are as previously defined. For example HORSO M may be sodium isethionate, HO(C-H SO Na; sodium hydroxypropane sulfonate, HO (CH SO Na; etc.

In a typical example of this reaction, equimolar amounts of pivalic acid and sodium isethionate may be heated in solvent medium, typically water, preferably in the presence of a catalytic amount of a catalyst, typically boric acid, and then heated further after volatilization of the solvent to say 200 C., thereby obtaining sodium 3-sul-foethylpival ate.

This invention may be further illustrated by the following examples which disclose synthesis of typical products of this invention and the use of such products as in the depression of surface tension in nickel plating baths. All parts are by weight unless otherwise indicated.

Example 1 A commercial mixture of neo-nonanoic acid, neodecanoic acid, and neo-undecanoic acid (sold under the designation Versatic 911 acid) may be reacted with 1,3- propane sultone and potassium hydroxide in methanol, to produce the potassium B-sulfopropyl acid ester as follows:

26 parts of potassium hydroxide dissolved in 88 parts of methanol may be slowly added to 50 parts of the acid, while agitated. 61 parts of 1,3-propane sultone dissolved in 20 parts of methanol may then be slowly added over a period of 15 minutes and the reaction mixture refluxed for five hours and allowed to cool, thereby resulting in a solid mass of a gel-like product. This may be heated slowly to redissolve, and placed on a steam bath under vacuum to volatilize methanol. The potassium salt of the 3-sulfopropyl acid ester may then be dissolved in 8 water, diluted to 500 parts and extracted with two 70- part portions of ether to recover and separate an ether solution of neutral oil.

The aqueous layer may then be evaporated down to 250 parts, and diluted again to 500 parts with water producing a clear light yellow solution of potassium 3- sulfopropyl acid ester. The ester may be obtained in substantially stoichiometric amount.

Example 2 A solution of 64- parts of 1,3-propane sultone (0.53 mol) in 400 parts of methanol may be added dropwise to parts of methanol containing 51 parts of pivalic acid (0.50 mol) and 20 parts of sodium hydroxide (0.53 mol). The reaction mixture may be agitated and held at reflux, over a period of about 6.5 hours. The reaction mixture may then be allowed to cool and the methanol then removed under vacuum. The residue may be diluted to 500 parts with water and impurities removed therefrom by extracting twice with ether. The remaining clear, colorless aqueous solution contains sodium 3-sulfopropylpivalate which is obtained in substantially stoichiometric amounts.

Example 3 78 parts of 1,3-propane sultone in 20 parts methanol may be added over a period of 15 minutes to a refluxing reaction mixture containing 86 parts of triethanolamine, parts of a commercial mixture of neo-nonanoic acid, nee-decanoic acid, and neo-undecanoic acid (sold under the designation Versatic 911 acid), and parts of methanol. The addition may be added over 15 minutes, after which the reaction mixture may be refluxed for 2 hours. The reaction mixture may be heated to drive off methanol, leaving a residue of 275 parts containing the triethanolamine salt of the 3-sulfopropyl acid ester as a mobile amber liquid in substantially stoichiometric amount.

Example 4 50 parts of the potassium salt of the S-sultopropyl acid ester obtained in Example 1 may be dissolved in 100 parts of methanol to which 18.7 parts of concentrated hydrochloric acid may then be added. The solution may be heated and aditated for an hour after which time a white precipitate forms immediately on addition of hydrochloric acid to produce substantially stoichiometric amount of the 3-sulfopropyl neocarboxylic acid.

Example 5 50 parts of a commercially available neo-nonanoic acid (sold under the designation Versatic 9 acid) may be dissolved in potassium hydroxide. 61 parts of propane sultone in 32 parts of methanol may be slowly added over a period of 5 minutes to a refluxing mixture of the acid in methanol. Refluxing may be continued for about 4 hours and the methanol then removed. The residue potassium 3-sulfopropyl neo-nonanoate, a thick viscous liquid obtained in substantially stoichiometric amount, may be dissolved in water and diluted to yield a slightly brown ish-yellow liquid.

Example 6 61 parts of propane sultone dissolved in 40 parts of methanol may be added dropwise over a period of twenty minutes to a refluxing commercial mixture of neo-pentadecanoic acid, neo-hexadecanoic acid, neo-heptadecanoic acid, neo-nonadecanoic acid (sold under the designation Versatic 1519 acid) in 80 parts of methanol containing 26 parts of potassium hydroxide. Reflux may be continued for three hours after the completion of the addition of the propane sultone. The reaction mixture may then be heated to volatilize alcohol. 162 parts of a gel-like product may be produced. This may be dissolved in 2000 parts of water. Neutral oil may be extracted from 100 parts of the foregoing solution with ether leaving a clear water layer. The ether layer may be evaporated to leave a residue of 0.8 gram of neutral oil. The remaining aqueous layer is a clear, colorless solution containing substantially stoichiometric amount of potassium 3-sulfopropyl neo-carboxylic acid} ester.

Example 7 To a standard Hull cell containing 267 ml. of a Wattsbath containing 300 g./l. of nickel sulfate, 60 g./l. of nickel chloride, 45 g./l. of boric acid, and having a pH of 4.0 (electrometric), 0.06 gram of the potassium 3-sulfopropyl neocarboxylate prepared by the process of Example 1 may be added. The surface tension of the electrolyte, as determined by a stalagmometer, may be observed to be depressed from 76 dynes/cm. to 58 dynes/cm. A highly polished brass cathode sheet may be plated for 10 minutes at 2 amps at a temperature of 54 C. The plated cathode may be observed to have a uniform white nickel plate which is substantially pit-free and striationfree over the conventional nickel plating range of to 12 amperes per square decirneter.

Example 8 Example 9 The solution of Example 7 may be modified by adding, as brightening agents, 4 mg./l. of thiodipropionitrile and 4 g./l. of 4,4-di-(Nsulfonylbenzene-sulfonamido) biphenyl. Plating a similar cathode under the same conditions as those of Example 7 results in a substantially pit-free and striation-free, bright, ductile deposit. No indication of any incompatibility of the bath components may be observed.

Example 10 The depression of the surface tension of 'a nickel plating b'ath containing 300 g./l. of nickel sulfate, 60 g./l. of nickel chloride, 45 g./l. of boric acid, and having a pH of 4.0 (electrometric) by adding increasing amounts of sodium 3-sulfo-propyl neo-carboxylate surfactant (prepared by reacting a commercial mixture of neo-nonanoic acid, neodecanoic acid, and neo-undecanoic acid sold under the designation Versati e 911 acid with 1,3-propane, sultone and sodium hydroxide as in the process of Example I) may be detennined as follows:

Grams of sodium 3-sulfopropyl neocarboxylate per liter: dynes/cm.

(a) 0.00 76 (b) 0.125 63 (c) 0.25 58 (d) 0.50 52 (e) 0.75 42 (f) 1.00 35 (g) 1.25 33 Pitting may be observed to be virtually eliminated on the cathode during nickel plating tests when at least 0.75 gram of the additive is present in the above nickel plating bath.

As many embodiments of this invention may be made without departing from the spirit and scope thereof, it

Surface tension in is to be understood that the invention includes all such modifications and variations as come within the scope of the appended claims.

I claim:

1. A process for electrodepositing nickel onto a basis metal which comprises passing current from an anode to a basis metal cathode through an aqueous acidic nickel plating solution containing at least one nickel compound providing nickel ions for electrodepositing nickel and containing as a surfactant, a compound, in an amount sulficient to reduce pitting, providing sulfohydrocarbon-di-yl neocarboxylate anion having the formula:

wherein R R and R are each alkyl groups and R is a hydrocarbon-di-yl group containing at least 2 carbon atoms.

2. A process for electrodepositing nickel onto a basis metal as claimed in claim 1 wherein said surfactant is a compound containing a bath-compatible cation selected from the group consisting of alkali metal and nickel.

3. A process for electrodepositing nickel onto a basis metal as claimed in claim 1 wherein R is a 2-8 carbon alk-di-yl group.

4. A process for electrodepositing nickel onto a basis metal as claimed in claim 1 wherein R is a 3-carbon alk-di-yl group.

5. A process for electrodepositing nickel onto a basis metal as claimed in claim 1 wherein said wetting agent is present to the extent of at least 0.125 g./l. of the solution.

6. A nickel plating solution comprising an acidic aqueous nickel plating solution including atleast one compound capable of providing nickel ions for electrodeposition of nickel and containing as a surfactant, a compound, in an amount sufiicient to reduce pitting, providing sulfohydrocarbon-di-yl neocarboxylate anion having the formula:

wherein R R and R are each alkyl groups and R is a carbon chain hydrocarbon-di-yl group containing at least 2 carbon atoms.

7. The nickel plating solution of claim 6 wherein said surfactant is a compound containing a bath-compatible cation selected from the group consisting of an alkali metal and nickel.

8. The nickel plating solution of claim 6 wherein said R is a 2-8 carbon alk-di-yl group.

9. The nickel plating solution of claim 6 wherein said R is a 3-carbon alk-di-yl group.

10. The nickel plating solution of claim 6 wherein said wetting agent is present to the extent of at least 0.125 g./1. of the solution.

References Cited UNITED STATES PATENTS 549,728 11/1895 Kraift et al. 260488 2,389,135 11/1945 Brown 204-49 X'R 2,389,179 11/1945 Brown 204-45 2,389,180 11/ 1945 Brown 204--49 XR HOWARD S. WILLIAMS, Primary Examiner.

G. KAPLAN, Assistant Examiner. 

